As you have been told that you need to first become a Jr Member at least in order to add a signature on your profile. Let me be more specific as to how you can reach that level. To become a Jr Member you have to earn Merits and also have a minimum of 30 activity.

To earn Merits you have to create topics in this forum that should be helpful and informative for other members as Merits can be only awarded to you by other members here.

Before posting here you should have read the rules on this board. In case if you have not read it yet then please click this link and read it  - https://bitcointalk.org/index.php?topic=1689727.0